Influence of molybdenum particles on thermal shock resistance of alumina matrix ceramics

The thermal shock resistance of Al 2O 3/Mo composites was investigated with emphasis placed on how the amount as well as the size of the metallic particles influence the resistance to thermal shock of these composites. Metal particles with two different average grain sizes were used. The composites, produced by hot-pressing, exhibited enhanced strengths and toughness but also lower Young's moduli as well as an increased thermal conductivity. The effect of molybdenum on thermal shock resistance arose from changes in thermal and mechanical properties of the composite. Twenty vol.% of molybdenum was found to be the minimum amount necessary to appreciably enhance toughness. In particular, the presence of coarse and elongated particles produced a better increase in toughness when compared with that of a composite added with finer particles. Metal particle bridging was the main responsible mechanism for toughness increase as well as for the reduction in thermal stress intensity factor. However, also changes in Young's modulus, thermal conductivity and thermal expansion played a role in the overall thermal shock behavior. Thermal shock severity as high as 450 °C was sustained in composites added with 20 vol.% of coarse molybdenum.